Black, white, and “green” – when it comes to the most cost-effective roof, what’s it all mean?

Published on February 7th, 2014 | By: Jessica McMathis

In the video above, former DOE Secretary Steven Chu explains the benefits of cool roofs. A new study by researchers at the Berkeley Lab found that white roofs, which are considered cool, are the most cost-effective option available. Credit: YouTube

What does the color of your roof say about you?

Perhaps nothing, but it may speak volumes for your pocketbook.

Researchers at the Lawrence Berkeley Lab have found that in comparing the economic costs and benefits of three different roof types—black, white, and “green” (vegetated)—white roofs are the most cost-effective.

In their report titled “Economic Comparison of White, Green, and Black Flat Roofs in the United States,” authors Julian Sproul, Benjamin Mandel and Arthur Rosenfeld of Berkeley Lab, and Man Pun Wan of Nanyang Technological University in Singapore compared the economic trade-offs between these three roof types by analyzing 22 U.S. commercial flat-roof projects that included a 50-year life cycle cost analysis.

Which roof won?

“White roofs win based on the purely economic factors we included, and black roofs should be phased out,” said Rosenfeld, distinguished scientist emeritus of the Berkeley Lab and former commissioner of the California Energy Commission, in a Berkeley Lab press release.

Green roofs, which have grown in popularity for aesthetic and environmental reasons, provide certain benefits not captured in the study, including stormwater management and the obvious benefit of green space for those who live or work under one of these rooftop gardens.

Regardless, these vegetated roofs do not offset climate change like white roofs, which reflect roughly three times more sunlight, and offset a portion of the warming effect from harmful greenhouse gas emissions.

White roofs reigned supreme in the study’s 50-year cost analysis, which found that even the most inexpensive green roof costs $7 per square foot more than black roofs— and that white roofs save $2 per square foot compared to black ones.

However, the study only includes economic results, and in their news release, the Berkeley Lab team acknowledges the need to consider other factors— such as health and environment—in future analysis.

“We’ve recognized the limitations of an analysis that’s only economic,” Mandel said. “We would want to include these other factors in any future study.”

For example, in cities where summer temps soar, black roofs pose major health risks. It’s why, according to Rosenfeld, policymaking is so important.

A supporter of “cool” roofs—which include white roofs that reflect sunlight, reducing energy costs and addressing global warming, and are used in roughly two-thirds of new roofs or roof-reinstallations—Rosenfeld was the co-author of a 2009 study that found that making roofs and pavements more reflective could offset 44 billion tons of CO2 emissions. Another study with similar results found that these cool roofs could offset emissions of roughly 300 millions cars for 20 years.